Tissue characterization of a vessel wall and presence/absence of stenosis are determined on the basis of, e.g., a vessel shape obtained by analyzing an image imaged by a modality such as an X-ray CT (Computed Tomography) apparatus and an MRI apparatus.
However, in order to analyze a shape of a tubular structure such as a blood vessel or tissue characterization of a wall of a tubular structure such as a vessel wall, it is required that a wall of a tubular structure is accurately specified. In conventional technology, a blood flow inside an examinee is imaged by using a contrast agent, then an inner wall of a vessel (i.e., vascular inner periphery) is positionally identified from the imaged blood flow, and then a position of a vessel wall is analyzed by estimating an outer wall of a vessel (i.e., vascular outer periphery) based on the identified inner wall of a vessel.